Capacitor



Patented Dec. 14, 1937 UNITED STATES CAPACITOR Leslie G. Burlingame, Erlton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 29, 1933, Serial No. 704,410

6 Claims.

My invention relates to fixed condensers and more particularly to condensers, of the type constituted by a plurality of foil-electrodes interrolled with strips of insulating paper orthe like, and methods of making and impregnating the same. 1

In radio receivers and similar apparatus, small by-pass condensers, filter condensers, blocking condensers and the like of small capacity, for example, .1 microfarad at 200 volts,'are extensively employed since space therefor is frequently at a premium and the condensers employed must therefore be as compact as possible in order to occupy a minimum of space.

It is frequently desirable, however, to employ condensers of the same size which have a much higher voltage and capacity rating, for example,

. .20 microfarad at 500'volts. It is known that the physical proportions of a. similar condenser increase with the square of a given voltage rating. For this reason similar condensers which have been subjected to a given impregnant and having a higher capacity and volt-age rating cannot occupy space which is sufiicient only for condensers having a much lower rating, for example, .1 microfarad at 200 volts.

It is, accordingly, an object of my invention to provide a condenser, of the character specified, which has a much higher capacity and voltage ratingfor'the same physical size as that of condensers known heretofore having a much lower voltage and capacity rating.

, Another object of my invention is to provide a condenser of the character specified, whose rated capacity remains substantially constant over a wide range of temperature, for example, minus 40 to plus centigrade.

A further object of my invention is to provide a condenser, of the character specified, which is hermetically sealed and which has a longer life than similar condensers of the same size used heretofore.

Another object ofmy invention is to provide a condenser, of the character specified, which has a greater dielectric strength and by reason of its greater uniformity is adapted to operate at higher voltages for the same paper dielectric as used in similar condensers of the'same size which are adapted to operate only at much lower voltages.

A further object of my invention is to provide a condenser, of the character specified, which permits of the use of high dielectric constant oils as an impregnating medium whereby ,a higher voltage and capacity rating is obtainable in a condenser of the same physical proportion.

Another object of my invention is to provide a condenser, of the character specified, wherein the condenser elements are shielded against stray losses.

A further object of my invention is to provide a condenser, of the character specified, wherein the body of the condenser is substantially surrounded by a high dielectric constant impregnating oil.

Another object of my invention is to provide a condenser, of the character described, which is readily assembled, cheap to manufacture, and wherein the elements, constituting the condenser, are protected against possible damage.

The foregoing objects and others ancillary thereto I prefer to accomplish as follows:

According to a 'preferred embodiment of my invention, I dispose within a section of suitable metallic tubing, having an internal lining of insulating material throughout its length, a complete but unimpregnated condenser element which is substantially smaller than the metallic tubing. Subsequently thereto, one end of the tube is sealed with one terminal member of the condenser extending outwardly of the sealed end thereof. The condenser is now impregnated with a high dielectric constant oil after which the remaining open end of the said tube is also sealed in a manner similar to the end previously sealed. Inasmuch as the diameter of the condenser body is less than the internal diameter of the insulated tube, a quantity of the impregnating oil surrounds the condenser whereby impregnation of the condenser is maintained, heat is conducted away from the condenser and the dielectric strength and capacity thereof maintained indefinitely.

With the above and other objects in view, the invention resides in the novelconstruction, combination, and arrangement of parts, the novel features of which are set forth with particularity in the appended claims. The invention itself,

' however, both as to its organization and its method of operation together with additional objects and advantages thereof, will best be understood from the following description of a Specific embodiment, when taken in connection with the accompanying drawing, in which:

Figure 1 is an enlarged sectional view of a fixed, condenser constructed in accordance with the invention and illustrating a preferred form thereof.

- Figure 2 is an enlarged sectional view taken on the line 2-2 of Figure 1.

Figure 3 is an enlarged sectional view illustrating a modified form of the condenser shown in Figure 1. i

Figure 4 is an enlarged sectional view taken on the line 4-4 of Figure 3.

Figure 5 is an enlarged sectional view illustrating a further modification of, the condenser shown in Figure 1.

Figure 6 is a fragmentary sectional view illustrating another modification of the condenser shown in Figure 1, and

Figure 7 is a similar fragmentary sectional view illustrating a still further modification with- 4 in the scope of my invention.

Referring more particularly to the drawing, wherein similar reference characters indicate corresponding parts throughout, a conventional form of fixed condenser, generally indicated at l0, comprises a plurality of insulating sheets and a plurality of sheets of metal foil wrapped therebetween, the metal foil sheets being spaced edgewise to present one marginal edge ll of each foil sheet beyond the marginal edges |2 of the insulating sheets l3.

The condenser I0 is provided at each end with a fiexible terminal connection or lead which is constituted by a single length of wire l4 bent upon itself substantially intermediate its ends and with the free end |5 of the bent portion I6 bent at right angles thereto.

The doubled end I! of each terminal wire l4 is inserted in the central opening I8 extending through the condenser l0 until each bent end l5 abuts the outer marginal edge II on each foil sheet whereupon each bent end I5 is secured in intimate contact with the foil sheets by means of solder or the like as fully disclosed in my copending application, Serial Number 657,336, filed February 18, 1933, and assigned to Radio Corporation of America.

In the manufacture of fixed condensers of the character referred to, it is known that when such a condenser is of a size whereby it is adapted to be inserted in a tubular paper container one and three quarters of an inch long having an internal diameter of five eighths of an inch, for example, and impregnated in a suitable mineral wax, a capacity up to .1 microfarad at 200 volts is obtainable.- Alternatively, if a similar condenser is disposed in a metal tube of the same size as that of the aforesaid paper tube and impregnated with an oil having the same dielectric constant as the aforesaid mineral wax, the capacity of the condenser is increased up to .1 microfarad at 500 volts. For the above purpose, a good grade of insulating mineral oil has been found to be satisfactory.

As a result of numerous experiments I have found that if a similar condenser is disposed in an insulated metal tube in spaced relation to the inner periphery thereof, then impregnated with castor oil, for example, having a higher dielectric constant than the aforesaid mineral wax and subsequently sealed, in accordance with my invention, a capacity of approximately .20 microfarad at 500 volts may be obtained without increasing the size of the condenser proper or altering the elements thereof.

In accordance with my invention, a preferred form thereof, referring to Figure 1 of the drawing, is constituted by a section of metal tubing 20 such as brass, for example, which is open at both ends. A section of insulating material in the form of a paper tube 2|,for example, having an outer diameter substantially equal to the internal diameter of the metal tube 20 and of slightly greater length, is disposed within the metal tube 20 in telescopic fashion as clearly shown in Figure 1.

A pair of cup-shape metal caps 22 having an outer diameter which is at least equal to the internal diameter of the paper tube 2| and which are each provided with a central opening 23, are adapted to be inserted in the open ends of the paper tube 2| by means of a press fit whereby the sections of tubing 20 and 2| are locked together and the open ends of the paper tube 2| closed for a purpose hereinafter described.

In practicing my invention, the paper tube 2| is so inserted in the metal tube 2|] that each end of the paper tube 2| projects an equal distance beyond the ends of the metal tube 20.

The condenser element indicated forthe purpose of my invention, has not been impregnated with any kind of wax or oil is now inserted in the .papertube 2| and one of the metal caps 22 passed over each of the terminal members or wires I4 and pressed into each open end of the paper tube 2| until the caps 22 are substantially flush with the ends of the metal tube 20. The outer periphery of each cap is substantially tapered so that the portion of the paper tube 2 I, between each cap 22 and the inner periphery of the metal tube 20, will be so wedged between each cap 22 and the metal tube 20 that an oil tight joint will be effected when each of said caps has been pressed into the ends of the paper tube 2| to the extent indicated in Figure 1.

At this stage in the assembly, the opening 23 in one of the caps 22 is closed by means of solder or the like, indicated at 24, whereby the terminal wire l4 extending through said cap 22 is also anchored thereto. The opening 23 in the other cap 22 disposed in the opposite end of the paper tube 2| is left open for the purpose of impregnating the condenser element I0. Accordingly, a plurality of condenser elements disposed in a plurality of tubes as described, are now disposed in a vertical position, with the unsealed cap openings 23 uppermost, in a suitable perforated container or the like which is then placed in an impregnating chamber where the condenser elements may be suitably evacuated and impregnated with a high dielectric constant oil. Immediately after the condenser elements I0 have been impregnated, the opening 23 in one of the caps 22 disposed in the ends of the tube 2|, is likewise closed by means of solder, as indicated at 24, whereby the opposite terminal wire I4 is likewise anchored to one of the caps 22 and the condenser element l0 hermetically sealed within the tube 2| with a quantity of impregnating oil, indicated at 25, surrounding the condenser element l0.

In one modification of my invention, shown in Figure 3, the condenser element l0, also in an unimpregnated state, is disposed within an open ended tube 26 of paper, for example, which is slightly longer than the length of the condenser element Ill. The open ends of the tube 26 are subsequently closed by means of cup-shape metal caps 21 which are pressed into the said open ends of the tube 26. The caps 21 are each provided with arectangular slot centrally thereof, as indicated at 28, whereby the marginal foil edges protruding from the ends of the condenser element Hi, and that portion of each terminal wire H5 attached to each of said foil edges, are exposed to permit said terminal wires M to project outwardly of said caps and to permit the impregnating oil to enter the tube 26 and to penetrate the condenser element l0.

at l0 which, I

The rectangular slot 28 in one of the caps 21 is now closed by means of solder, as indicated at 29, and the condenser element l0 subsequently impregnated with a high dielectric constant oil in the manner described in connection with Figure 1. After impregnation of the condenser element l0 has been completed, the slot 28 in the opposite cap 21 is also closed by means of solder whereby the terminal wires I4 are each anchored to the caps 21 and a quantity of the impregnating oil maintained within the tube 26 and about the condenser element III as indicated at 29.

Finally, a second paper tube 30 of greater length and having an internal diameter substantially equal. to the outer diameter of the tube 26, and which has been impregnated with a suitable wax which solidifies at room temperature, is now passed over the tube 26 and its open ends closed by means of a suitable compound 3|.

Referring to Figure 5, wherein a further modification of my invention isillustrated, I substitute an extruded metal cylinder 32, having a length and internal diameter substantially greater than the diameter and length of the condenser element l0, and a small opening 33 formed centrally of its closed end 34, for the open ended metal tube 20 shown in Figure 1.

As in the preceding embodiments of my invention, an insulating tube 35 of paper, for example, having an outer diameter substantially equal to the internal diameter of the cylinder 32 and of a length substantially equal thereto, is inserted therein.

A complete but unimpregnated condenser element l0, having a maximum diameter substantially less than the internal diameter of the insulating tube 35, is then disposed within the said tube 35 with the terminal wire i4, attached to the inner end of the condenser element l0, extending through the opening 33 in the closed end 34 of the cylinder 32.

A cup-shape cap 36, similar to those shown in Figure 1, and having a small opening 31 centrally thereof and a tapered outer diameter at least equal to the internal diameter of the insulating tube 35, is next passed over the opposite terminal wire I4 and forced into the exposed open end of the insulating tube 35 in a manner identical with that described in connection with Figure l.

The small opening 33 in the cylinder 32 is now closed with solder, as indicated at 38, and the condenser element l0 subsequently impregnated with a high dielectric constant oil. The small opening 31 in the cap 36 is thereafter closed by means of solder whereby the terminal wire i4, extending through the opening 31, is anchored to the cap 36 and a quantity of impregnating oil surrounding the condenser element I 0, as indicated at 33, sealed within the tube 35.

In connection with Figures 1 and 5, it is to be observed that the metal caps 22 and 36 do not contact with the metal tube 20 and cylinder 32 by reason of the interposition of the insulating tubes 2l and 35 therebetween whereby the caps 22, 36, and the oppositely disposed terminal wires l4 are insulated from each other and at the same time an oil tight joint is effected between the metal tube 20, the metal cylinder 32 and the metal caps 22 and 36 respectively.

Inasmuch as the metal caps 22 as shown in Figure l, for example, are insulated from eachother and the metal tube 20, it is also within-the scope of my invention to dispose a fixed condenser element within the insulating tube 2| which is not provided with terminal members or leads such as those indicated at l4, for example, since I may insert the metal caps 22 in the respective ends of the insulating tube 2| to a depth where they will contact directly with the protruding marginal foil edges ll of the condenser element 10 as illustrated in Figure 6 and thereby serve as terminal connections for the condenser element after it has been impregnated in the manner herein described and the openings in the metal caps sealed.

My invention is also applicable, for example, to a relatively large metal can or container 40, as illustrated in Figure 7, which is adapted to receive a plurality of fixed condenser elements ID of known form together with an impregnating oil as described and which is provided with a suitable closure member or lid 4i permanently attached to the container.

In such a container, the metal closure member or lid 4| is, in accordance with my invention, provided with a plurality of spaced, relatively large openings 42 in which a plurality of metal caps 22, as illustrated in Figure 1, may be frictionally inserted together with an insulating bush ing or sleeve 43 to maintain said caps out of coni tact with said closure member or lid whereby to provide terminal members to which terminal leads, carried by one end of each of said condenser elements, may be secured in the same manner in which the terminal leads I 4 (Figure 1) are secured by closing the central openings in the caps about the terminal members by means of solder. The opposite end of each condenser element l0 contacts directly with an inner surface of the container whereby the said container provides a terminal connection common to one end of all of said condenser elements.

, From the foregoing, it will become readily apparent, to those skilled in the art, that I have provided a condenser construction which is cheap to manufacture, easily and quickly assembled and which is highly efficient for the purpose for which it is designed.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. stricted except insofar as is necessitated by the prior art and the spirit of the appended claims.

I claim as my invention:

1. In combination, a metallic container having a plurality of openings therein, a container of insulating material disposed within said metallic container in contacting relation therewith and having a plurality of openings therein registering with the openings in saidfirst named container,

,a fixed condenser element having terminal leads attached to the opposite ends thereof disposed within said second named container in spaced relation thereto, a pair of metallic closure, members each having a central opening therein disposed in the openings in said second named container with said terminal leads projecting through the openings in said closuremembers, a liquid dielectric impregnating said condenser element and filling the space between said insulating container and said condenser element, and means for sealing the openings in said closure members about said terminal leads.

2. In combination, an open ended metallic tube, an open ended tube of insulating material disposed within said metallic tube, a fixed condenser element disposed within said insulating tube, a

'each open end of said insulating tube, a pair of terminal leads attached to the opposite ends of said condenser element and extending through said cap openings, 2. liquid dielectric impregnating said condenser element and filling said insulating tube, and means for sealing said cap openings about said terminal leads.

i 3. In combination, a metallic tube, a'tube of insulating material disposed within said metallic tube in contacting relation therewith, a fixed condenser element disposed within said insulating tube in spaced relation thereto, a pair of metallic caps each having a central opening therein and each secured in the respective ends of said insulating tube, a pair of terminal leads attached to the opposite ends of said condenser element and extending through said cap openings, a liquid dielectric impregnating said condenser element and'filling said insulating tube, and means for sealing said cap openings about said terminal leads.

4. In combination, a metallictube, a tube of insulating material disposed within said metallic tube in contacting relation therewith and with its ends projecting substantially outwardly of the ends of said metallic tube, a fixed condenser elecap openings about said terminal leads.

5. In-a condenser, an open ended metallic tube,

- a condenser element disposed within said tube in spaced relation thereto and being of shorter length than said tube, said condenser element being spi-- rally wound and having exposed marginal foil edges, an open ended tube of insulating material within said casing, said insulating tube surrounding but being also spaced from said condenser element, a pair of cap members each having an opening therein and adapted-for closing the open ends of said insulating tube, a liquid dielectric surrounding and impregnating said condenser element, said dielectric being disposed within and filling the space between said cap members and between said condenser element and said insulating tube, a terminal wire secured to each of said foil edges and extending through the opening in the adjacent cap member, and means for sealing the opening in said cap members about said terminal wires.

6. In combination, a metallic container comprising an open ended tube, an open ended tube of insulation material disposed within said first mentioned tube with its free ends extending slightly beyond the ends thereof, a fixed con denser element having exposed marginal foil edges disposed within said inner tube, a pair of cupshaped metal caps, each force fitted into the respective openings in said insulating tube with said marginal foil edges contained within said cup-shaped caps, a liquid dielectric contained within said insulating tube and impregnating said condenser element, the outer surfaces of said cup-shaped caps contacting said insulating tube substantially throughout their length to effect the wedging of a substantial area of the end portions of said insulating tube against the inner surface of said metallic container whereby to provide a fluid tight seal.

LESLIE G. BURLINGAME. 

